Remembering why I
dislike working on
AO Silver Member
Join Date: Sep 2001
Won't matter mate, the ECU will store the code for you - it's good like that. It only erases an error code after an ECU reset (battery off for a few minutes), or after 50 successful engine starts with no repeat error.
I hope the folk you are using are reputable though. When I first got my car and had the warning light come on, I didn't know it was possible to poll the code myself so took it to a local 'specialist'. He told me he had to order in the module for his tester. Eventually went back for the car and he said no fault found. In reality, he never even bothered looking 'cos he couldn't be ar5ed to get the module.
I haven't looked into this for the 155, but on early 164s, some didn't have a diagnostic button & lamp. It's very easy to add one on those - did it on my old '91. Later ones either had a button or used the same method as some 155s - the 'pump-pedal-5-times' technique.